This invention relates generally to precision motion devices. More particularly, this invention relates to precision motion devices that can be made of non-metallic materials and that can be used in a vacuum environment. Even more particularly, this invention relates to precision motion devices that have drive actuators located outside the stage and vacuum chamber.
Precision motion devices are well known; they are typically used in machine tools and other applications where two-dimensional precise movement is needed to position an object. One application of a precision motion device is as an xy stage used in lithography equipment for the manufacture of semiconductor integrated devices. In lithography systems, an xy stage is typically used to position in two dimensions either a reticle (mask) or a semiconductor wafer. A lithography system includes a source of radiant energy for illumination such as a mercury lamp or other types of lamps or laser or electron-beam sources and a lens system to focus the radiation, which is directed through the reticle onto a substrate such as a semiconductor wafer. The lens system in a photolithography system is an optical lens system and in an electron-beam lithography system the lens system is an assembly of magnetic coils and/or electrostatic elements.
As current semiconductor integrated devices have become more complex and smaller, the required accuracy of the precision motion devices has had to be substantially increased. Such accuracy may be achieved by, for example, electron-beam lithography systems. However, electron-beams can be degraded by dynamic variation in magnetic fields. Such varying fields can be caused by disturbances in the magnetic field along the lens axis. These variations can be caused by, for example, stray magnetic fields, moving magnets, or moving iron (or, to a lesser extent, any moving metal) within the earth""s or the lens"" magnetic field. A typical xy stage is mechanically scanned back and forth in one direction such as the x-direction and is mechanically stepped in the orthogonal direction such as the y-direction. In order to mechanically scan and step the stage, it is typical to utilize electric linear motors that have motor coils attached to the stage and permanent magnets attached to a supporting structure. Other electromagnetic effects can detrimentally affect the magnetic field in the lens axis (i.e., where the electron beam is). Typical examples of such variations in the magnetic fields include, but are not limited to:
(a) moving magnets;
(b) moving coils with electric current flowing through them;
(c) fixed coils with alternating current flowing through them;
(d) moving conductive materials in which eddy currents form as they move in a non-uniform magnetic field; these eddy currents in turn create new magnetic fields; and
(e) iron materials which change position and thereby alter the external magnetic fields created by the electron lens optics or the earth""s magnetic field.
In order to avoid these, and other, detrimental effects, added complexity must be added to the typical stage. For example, the linear motors must be located as far as possible from the electron beam and must be located symmetrically to cancel the magnetic fields created by the permanent magnets.
Accordingly, there is a need for an xy stage assembly that has drive actuators that are external to the xy stage and that are driven by motors that are also located externally to the xy stage allowing the xy stage chamber to provide magnetic shielding.
The present invention overcomes the above problems of prior art xy stage assemblies and provides other additional advantages through a method and apparatus for providing precise xy motion to an xy stage.
In one aspect of the invention an xy stage has at least one support shaft and at least one preload shaft wherein at least one of either the at least one support shaft or the at least one preload shaft is a drive shaft driving the xy state in the x direction.
Each of the at least one support shaft and each of the at least one preload shaft is supported by first and second bearings that are individually translatable in the y-direction to provide yaw to the xy stage and are individually translatable in the z-direction to provide either pitch, roll or uniform z-direction displacement to the xy stage.
In another aspect of the invention an xy stage has at least one support shaft and at least one preload shaft where at least one of either the at least one support shaft or the at least one preload shaft is a drive shaft driving the xy stage in the x direction. Each of the at least one support shaft and each of the at least one preload shaft is supported by first and second bearings that are collectively translatable in the y-direction to drive the xy stage in the y-direction.
In accordance with another aspect of the invention, either the at least one preload shaft or the at least one support shaft has at least one wheel that contacts the xy stage.
In accordance with still another aspect of the invention, the at least one wheel rides in a groove in the xy stage.
In accordance with another aspect of the invention, either the at least one preload shaft or the at least one support shaft has at least one groove in the circumference of the shaft and the xy stage has a rail on which the at least one groove in the shaft rides.
In accordance with another aspect of the invention, the xy stage is supported kinematically by the at least one preload shaft and by the at least one support shaft.
In accordance with another aspect of the invention, the xy stage is divided into two sections that are joined by a compressive layer.
In accordance with another aspect of the invention, the xy stage has a compliant contact layer on the surface of the xy stage on which the shaft rides.
In accordance with another aspect of the invention, a separate drive system drives a belt that is disposed between the xy stage and the support shafts.
The described xy stage assembly thus provides a friction drive xy stage that is precisely driven in x and y directions by drive shafts and that can have applied to it a pitch, a roll, an uniform z-axis displacement and a yaw. In addition, all sides of the xy stage can be polished mirrors to allow laser interferometer position measurements from all sides of the xy stage.
These and other advantages of the present invention will become more apparent upon a reading of the detailed description of the preferred embodiments that follow, when considered in conjunction with the drawings of which the following is a brief description. It should be clear that the drawings are merely illustrative of the currently preferred embodiments of the present invention, and that the invention is in no way limited to the illustrated embodiments. As will be realized, the invention is capable of other embodiments and its several details are capable of modifications in various obvious aspects, all without departing from the scope of the invention. The present invention is best defined by the claims appended to this specification.